Animating bones through blueprint - what am I doing wrong?

Screenshot 2017-01-10 17.05.02.jpg
So I’m trying to set up some random animation on a mesh by scaling certain bones using a timeline. The plan is to set up a loop that would then apply random settings for each bone automatically, but I cannot for the life of me make it work properly. It seems to be recalculating each tick - all the random numbers keep updating, and the Playback Position node seems to fire continuously as well. I’m GUESSING at least some of it is because I am doing it in the Event Graph instead of the Construction Script - but I can’t figure out how I’d split it up. I’m sure there’s an obvious solution I’m missing - anyone have any ideas or insights?